Electric motors can be of two types: synchronous motors and induction motors. Furthermore, based on the difference in rotors, the motors can be classified into motors of a magnet type using permanent magnets, motors of a winding type comprising wound coils, and motors of a reactance type using a ferromagnetic body such as iron. In the motor of a magnet type, the permanent magnet of the rotor is pulled into the rotary magnetic field of the stator and rotated.
A small synchronous motor described in Japanese Patent Application Laid-open No. H8-51745 is an example of a magnet-type synchronous motor. This small synchronous motor comprises a stator core having an excitation coil wound thereabout and a rotor comprising a magnet.
However, the problem associated with the conventional motors was that the weight increased proportionally to the generated torque and an attempt to increase the generated torque resulted in increased size.